There is no "twice as loud". SPL (sound pressure level) is measured in decibel. 60 db is the level of normal human speech. 120 dB, which is twice as loud, is the level of a jet aircraft taking off. If you are directly underneath that jet at the time, there is a good chance of getting killed by that level of sound. The level of a stadium rock concert is about 115 dB, and it is known to cause permanent hearing damage in some people. To put it in perspective for you, for an increase of volume by 3 dB the amplifier power must double. So, +9 dB increase of volume means 8 times increase in amplifier output power (2 x 2 x 2). Similarly, your current phono gives you 36 dB vs. suggested 47 dB - see now why your volume is so anemic now? It's 11 dB below the suggested figure.